This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of any prior art.
Many diesel fuel formulations contain cetane improving additives, also known as cetane boosters, cetane improvers or ignition improvers, to increase their cetane numbers. The cetane number of a fuel is a measure of its ease of ignition. With a lower cetane number fuel, a compression ignition (diesel) engine tends to be more difficult to start and may run more noisily when cold. There is a general preference therefore for a diesel fuel formulation to have a high cetane number, and as such automotive diesel fuel specifications generally stipulate a minimum cetane number.
Typically, cetane improving additives are used in the form of an additive package which contains one or more functionally active substances in a suitable solvent vehicle.
It is often desirable to reduce the concentrations of additives in diesel fuel formulations. This may be driven by consumer preferences and/or by technical or economic considerations. In cases it may be driven by a desire to reduce side effects associated with a particular additive, or with an interaction between two or more additives which are present in a fuel formulation.
Efforts to achieve reduced additive levels have tended to focus on providing additives with higher activities, or synergistic combinations of additives, or additives with higher stabilities which can thereby provide performance-enhancing benefits for longer periods. Attempts have also been made to control the release of additives into fuel formulations, so as to enhance their effects at a location or time point where they can be most useful: such attempts include the incorporation of additives into insoluble gels, polymers and other solid matrices (eg WO 2010/132209, WO 2010/014528, WO 2006/105025, WO 2005/123238, WO 2005/052096, WO 2005/003265, WO 2003/083017, WO 2003/018727, WO 02/00812, WO 99/40166 and U.S. Pat. No. 4,515,740); their immobilisation onto filter supports (WO 2003/018988) or ion exchange resins (U.S. 2005/0035045); their encapsulation in lipid vesicles (WO 2000/49108) or microcapsules (JP 1210497 and WO 2003/004146); and even their delivery via dispensing containers, as described in WO 2003/018726.
According, there is still a need for alternative forms of cetane improving additives which can be used at lower levels and/or which can more efficiently modify the properties and/or performance of a diesel fuel formulation.